I saw the article titled "Memory test - Firefox 2.0.0.9 vs Firefox 3.0 b1". I am interested in that kind of browser comparison, so I clicked at the screenshots there.

But, to my disappointment, the memory usage that is measured is determined by "Memory Usage" column of Windows Task Manager. It is NOT the correct method of measuring memory usage, because it only indicated how much memory is "active", not the total memory allocated by the program. To get how much memory allocated, the correct column is "VM Size" in XP or "Commit Charge" in Vista. Actually programs such as TaskInfo are able to reduce the "Memory Usage" of any program (e.g. 5 MB only for Firefox 2). Hence, "Memory Usage" is not a good measure for memory usage.

So, I ran a test of Firefox 2, Firefox 3 beta 1, Opera 9, and Internet Explorer 7 to see the real memory usage. As a bonus, Javascript speed test is added from Celtic Kane.

I ran all the test in an almost-clean Windows XP installation. Firefox's profile directory were set differently for Firefox 2 and 3. Screenshots with Task Manager open are always available :) No plug-ins (even flash) or extensions were installed!

Step 0 - install

	Firefox 2	Firefox 3	Opera 9	IE 7
Installer name	Firefox Setup 2.0.0.9.exe	Firefox Setup 3.0 Beta 1.exe	Opera_9.24_Eng­ _Setup.exe	IE7-WindowsXP­ -x86-enu.exe
Installer size	5.74 MB	6.40 MB	4.69 MB	14.7 MB
Installed size	19.9 MB	22.8 MB	4.81 MB (yeah!)	Who knows?

Step 1 - blank

I set the browser's start-up page to be blank. Then I started the browser and here are the memory usage.

	Firefox 2	Firefox 3	Opera 9	IE 7
VM Usage	11,672 KB	13,076 KB	12,568 KB	11,616 KB
Screenshot

IE is the best for blank page (HEHE)

Step 2 - Google only

I opened www.google.com which redirected me to www.google.com.sg since I am currently in Singapore.

	Firefox 2	Firefox 3	Opera 9	IE 7
VM Usage	12,152 KB	13,432 KB	14,056 KB	15,128 KB
Screenshot

Here we can see the worseness of IE starts to appear.

Step 3 - Digg only

Why Digg? Because it is loaded with lots of Javascript.

	Firefox 2	Firefox 3	Opera 9	IE 7
VM Usage	18,700 KB	22,280 KB	19,780 KB	30,920 KB
Screenshot

I am quite disappointed knowing that Firefox 3 is not better in terms of memory usage than Firefox 2. IE? WOW.

Step 4 - open 7 and 12 sites and a digg page

I tried to open 7 sites below:

• www.yahoo.com
• www.cnn.com
• www.opera.com
• www.firefox.com
• www.netcraft.com
• www.slashdot.org
• www.amazon.com

After all are loaded, I clicked on each of the 7 tabs two times to let the browser actually draw the page elements on screen. Then I opened 5 more sites below and clicked each of them again.

• www.bbc.co.uk
• www.detik.com
• www.kompas.com
• www.cnet.com
• www.kejut.com

I added one more, which is the digg page for the ZDNet's memory test, but this time I clicked the "Expand Tree" to make the page very long and Javascript-intensive.

I calculated the difference in memory usage before and after opening the last page.

	Firefox 2	Firefox 3	Opera 9	IE 7
After 7 sites	40,556 KB	45,320 KB	44,284 KB	71,120 KB
Screenshot
After 12 sites	59,648 KB	59,068 KB	65,492 KB	99,936 KB
Screenshot
After add last page	73,540 KB	73,244 KB	75,800 KB	119,748 KB
Increase in memory	13,892 KB	14,176 KB	10,308 KB	19,812 KB
Screenshot

Only after opening 12 pages then Firefox 3 uses less memory than Firefox 2? I wonder why. Opera has the lowest increase of memory when opening the last page. I think because Opera is still very efficient in the Javascript processing.

Step 5 - clean up

After the previous step, I closed all the 12 tabs, and I set the last tab to about:blank. I wanted to know how much the browsers clean up the memory. Result:

	Firefox 2	Firefox 3	Opera 9	IE 7
VM Usage	46,952 KB	55,936 KB	61,588 KB	56,860 KB
Screenshot

I hoped this was the best thing in Firefox 3, but my hope was wrong! Firefox 3 still consumed much more memory than Firefox 2. WHY? I don't know. Opera, as I expected, still used much memory, because I can click the trash-can and open closed tab, and the opening will be very fast, looks like the pages are still in memory.

Bonus - Javascript speed test

I wondered, did the Firefox developers made Javascript execution faster in Firefox 3? At least I can be proud of it if they did. So I used the test from Celtic Kane to measure it.

	Firefox 2	Firefox 3	Opera 9	IE 7
VM Usage	15,520 KB	16,696 KB	15,920 KB	22,392 KB
Total Duration	1832 ms	2974 ms	931 ms	1262 ms
Relative to Opera	1.97 times	3.19 times	1.00 times	1.36 times
Screenshot

Nothing interesting about the memory usage... but !? how come Firefox 3 is very slow? I tried not only once, but more than five times and it was still about the same.

Conclusions

Firefox 3 does not uses less memory than Firefox 2. It also does not clear unused memory when all the pages are closed. However, both Firefox 2 and 3 are still conservative compared to IE 7. It is surprising that Firefox 3 is significantly slower in Javascript execution than Firefox 2.

Opera uses slightly more memory than Firefox, and IE is really a memory hog. When switching tabs I needed to wait about ~0.4 seconds in IE but it was instant in Firefox and Opera.

I still have the test machine unmodified by this time, if anyone want to suggest a test that would be better reflects the better memory management of Firefox 3, please write down below. Suggestions and comments are happily welcomed! ↓